Technical Field
The present disclosure relates generally to the field of pipe coupling treatment systems, and methods of use, and more specifically to pipe coupling ovens thermal cleaning and coating ovens (systems), and methods of their use, particularly for producing internal or externally coated pipe couplings.
Background Art
It is a common practice to coat and apply protective coatings to pipes of all sorts, such as line pipes, which are buried underground, to move gasses or liquids from point A to point B. The pipe may have diameter anywhere from 2 inches, all the way to 48 inches or more and have either internal or external coatings applied, depending on the application, for corrosion protection or ease of flow. For example, line pipes and drill pipes typically have internal coated pipes to minimize friction for easy flow of fluids and have corrosion protection with the inner coating of the pipes. There are several service companies in the business of applying internal coatings to the pipes, including line pipes as well as the drill pipes.
In a typical process, a phenolic coating is applied internally, and baked on at 450-500° F. The process of coating the pipe, is typically as follows:                First Stage: burn off the old coating or oils. Sometime termed “pre-bake”, “burn off” or “pre-heat”, the pipe is heated to 750° F. to either burn off the old coatings on used pipe, or burn off the oils on new pipe. This process is also sometimes referred to as “thermal cleaning” of the pipe. One older technique used to be to heat up the pipe in a burn off oven, overnight, generally about 24 hours. Aziz Jamaluddin, one of the inventors of the present patent application, and president of Epcon® Industrial Systems, LP (formerly known as Entech Industrial Systems) obtained several U.S. Pat. Nos. 4,240,787; 4,242,084, and 4,322,203, allowing this thermal cleaning process to be reduced significantly in time.        Second stage: sand blasting. After thermal cleaning, the pipe is internally sandblasted to white metal and then coatings are applied in two to three stages, either liquid or powder.        Third stage: application of coating. The pipe from Stage 2 would then roll into a separate conveyorized “bake” oven, two or three in a row, each bake oven being preceded by an internal coating station. The bake oven temperature is 400-500° F.        Fourth stage: the final bake.        
Along with the pipe, there are pipe couplings of various sizes—anywhere from 2.5 inch, 6 inch, 8 inch, 12 inch and up to 16 inch in diameter. Like the pipe, the couplings need to be thermally cleaned, typically at temperatures about 750° F., a coating is then applied, and then cured at 450-500° F. This task is accomplished by putting the couplings in one or more open containers or baskets inside the burnout oven and heating it for several hours or overnight at 750° F., and then the next day the couplings have the powder or liquid applied, and are then put in a different oven, operating at 450-500° F.
Various types of ovens and methods are used for the above, all generally comprising a box or container defining a treatment zone, heating apparatus such as burners for direct heating of circulating air, air circulation fans, and exhaust fans. Due to the temperature difference between the thermal treatment and the coating bake steps, separate ovens are used. The above-mentioned '203 patent describes one such thermal cleaning oven, including an elongated rectangular framework supporting a plurality of insulated panels. The supporting framework comprises a plurality of vertically extending structural steel supports, longitudinally and horizontally extending supports, and laterally and horizontally extending supports. The supports comprise steel H-beams or the like and are preferably joined by welding into a rigid framework. The oven is enclosed by longitudinally extending, vertical side walls consisting of thick-walled insulated panels, and a longitudinally extending top wall, consisting of a thick-walled insulated panel. The oven is open at one end for introduction of pipe to be processed and has a vertically sliding end door supported for vertical movement between vertical supporting H-beams. A pair of rails extend longitudinally of the oven which support the wheels of a cart for movement of a load of pipe into and out of the oven. The oven chamber or enclosure is supported from the top portion of the frame, consisting of supports and a series of shorter, the vertically extending H-beam supports which also support horizontally extending, bottom insulated panels. Obviously, these specifications can be varied, as needed, but represent a typical commercial installation. The oven has plenum chambers extending longitudinally thereof on opposite sides of the rails, each plenum chamber having a plurality of vertical slots or nozzles spaced along the entire length thereof for directing flow of heated air horizontally on to the pipe on the cart. The supply of heated air for heating the pipe to burnout temperature and the control of air pollution from the pipe burnout and recovery of waste energy are provided by equipment carried on top of the supporting frame for the oven, including burners which draw air from the oven and heat it. The heated air is recirculated to the oven by blowers. Air is exhausted slowly from the oven by an exhaust fan or blower through an incinerator, where hydrocarbon byproducts are consumed. A heat exchanger is used to heat incoming combustion air for the burner section. The air from the heat exchange section is exhausted by the blower to atmosphere. The burner section comprises a rectangular chamber enclosed by insulated panels (the side walls, end walls, top wall, and bottom wall), the sidewalls having openings in which there are positioned burners. The bottom wall of the burner chamber has a central opening, which opens into the top of the elongated oven enclosure.
During most of the operation of oven of the '203 patent, the burner chamber central opening is the only opening for circulation of air from the oven into burner chamber. End walls of the burner chamber have openings in which there are secured the inlet end and outlet end of a heat exchange conduit. This takes some of the heat away from the combustion gases from the burner that otherwise could be used to heat the pipe. The end walls of the combustion chamber also have openings for connection to the inlet sides of the recirculation blowers, which in turn have their respective outlets connected by conduits to the vertical, oppositely opposed plenum chambers. The apparatus described in the '203 patent is a batch type pipe burnout oven with air pollution control and heat recovery features.
As noted herein, the predominant technique is to employ separate ovens for thermal cleaning and coating baking, employing direct-heated air in cross-circulation flow of the air through pipes or couplings being treated, where flow direction of heated air onto the pipe or couplings (generally horizontal) is directed by side-mounted heated air plenums. While fairly efficient, this technique requires a lot of floor space due to the use of separate ovens. This limits the applicability of the technique to operations where separate ovens are available, or to use of the same oven in different operating temperature regimes, which would also be counterproductive.
It would be an advanced in the pipe coupling treatment art, and in particular the art of combustion-based thermal cleaning and coating baking, to provide a more compact, conveyorized, simplified oven having two or more treatment chambers, saving time, labor and space energy usage.